Field of the Invention
The present invention relates to a wireless power supply device and a wireless power supply system, and more particularly, it relates to a wireless power supply device and a wireless power supply system each including a resonance circuit.
Description of the Background Art
A wireless power supply device including a resonance circuit is known in general, as disclosed in Japanese Patent Laying-Open No. 2011-182012.
Japanese Patent Laying-Open No. 2011-182012 discloses a noncontact setting device (wireless power supply device) including a resonance circuit constituted by a power transmission coil that supplies power to a device to be set (receiver) in a noncontact manner and three capacitors connected in series to the power transmission coil. This noncontact setting device is configured to change the resonant frequency of the resonance circuit by changing the number of capacitors connected to the power transmission coil (to one, two, or three) by switches. Thus, in this noncontact setting device, the resonant frequency for optimally transmitting power is selected according to a power transmission distance (a distance between coils) to the device to be set.
In general, it is known that the resonant frequency of a resonance circuit of a wireless power supply device is changed due to temporal change, usage environment, etc. In this case, the resonant frequency of the resonance circuit is deviated from a desired resonant frequency. Consequently, the efficiency of power transmission from the wireless power supply device to a receiver is disadvantageously reduced due to change of the resonant frequency of the resonance circuit of the wireless power supply device.
In order to resolve the aforementioned disadvantage, the approach of the noncontact setting device described in Japanese Patent Laying-Open No. 2011-182012 is conceivably employed. More specifically, the resonant frequency of the resonance circuit of the wireless power supply device is conceivably changed by changing the number of capacitors connected to a power transmission coil by switches to correspond to change of the resonant frequency of the resonance circuit resulting from temporal change, usage environment, etc.
In this case, however, three capacitors must be provided to adjust change of the resonant frequency of the resonance circuit resulting from temporal change, usage environment, etc. Thus, the resonance circuit is disadvantageously increased in size and complicated in structure.